1. Field of the Invention
The present invention relates to road white line recognition apparatus and method to recognize a road white line used for displaying a traffic lane divisional zone on a road surface on which the vehicle travels.
2. Description of the Related Art
Various techniques for recognizing a road white line (or road white lines) through a monitor image and a relationship between the vehicle and the road white line is used for a vehicular automatic control or partially for an automatic control (for example, a vehicular velocity control system or a vehicular lane keep control system) have conventionally been proposed.
A Japanese Patent Application First Publication No. Heisei 5-347000published on Dec. 27, 1993 discloses a previously proposed road white line recognition apparatus. In the disclosed road white line recognition apparatus, white line candidate points constituting each road white line are detected from the photographed image and a road shape or a posture of photographing means such as a camera to obtain the photographed image is estimated on the basis of positional coordinates of the white line candidate points. At this time, a processing region (hereinafter, referred to a threshold value calculating region) to calculate a luminance (or gray level) threshold value of the photographed image used to extract white line candidate points is set by threshold value calculation region setting means, a position and a range of the threshold value calculating region are dynamically varied, and the threshold value of the luminance of the photographed image used to extract the white line is calculated by a combination of a maximum value and an average value of the luminance in the threshold value calculating region so that an assured extraction of the road white line can be achieved even if a contrast of the photographed image is varied.
In details, as described above, whenever the photographed image is inputted, the luminance threshold value of the photographed image used to extract the white line from the photographed image is calculated. Hence, the luminance threshold value used to extract the white line is dynamically updated. Thus, with respect to a variation in a contrast on a road image, a capability of extracting the white line from the photographed image is optimized. Hence, even if the contrast between the white line and road surface is varied due to such a change in a quantity of light of a surrounding of the road surface as is found in a difference in a day time and in a night time, a variation in a white line detection capability can be reduced.